Ontogeny: development of an individual
from the moment the egg is fertilized up till adulthood.Opaque area: non-transparent part.Pellucid area: transparent part.Neural fold: fold related to the head.Neural tube: extension related to the head.Heart: blood-pumping organ.Somites: metameres.Omphalomesenteric arteries: vitelline duct.Wing buds: beginning of the formation of the wings.Limb buds: beginning of the formation of the legs.